The present invention relates to novel magnetic recording compositions and to magnetic recording media employing them. More particularly, it relates to magnetic recording compositions containing an ionic dye-reactive counter ion complex as a photoinitiator.
Magnetic recording media exist in the form of magnetic cards and disks, reels, video tapes, and computer tapes. Magnetic tape, for example, is utilized for audio, video, computer, instrumentation, or other recordings. Magnetic tape consists of a magnetic recording composition on a support film. Typically, the magnetic recording composition contains magnetized particles which store information and a resinous binder which provides the cohesive matrix between the magnetic particles and adheres the magnetic particles to the support film.
Solvent-based magnetic recording compositions which are thermally curable are known in the art. For example, U.S. Pat. No. 4,122,234 teaches a composition comprising epoxy resin, polyamine, cellulose acetate butyrate resin, magnetic ion oxide particles, and solvent. The composition is coated onto a substrate and cured at temperatures of about 210.degree. to 240.degree. C. Also, see U.S. Pat. No. 4,609,588.
Solvent-based magnetic recording compositions which are electron beam curable are also known. For example, U.S. Pat. No. 4,607,068 teaches a composition comprising a polyethylenically unsaturated polyurethane oligomer, magnetic pigment, and solvent. The composition is coated onto a substrate and the solvent is allowed to evaporate. The composition is then cured by exposure to election beam radiation. Also, see U.S. Pat. Nos. 4,468,436; 4,496,686; 4,503,198; and 4,634,633.
Solvent-based magnetic recording compositions which are ultraviolet or visible light curable are also known. For example, U.S. Pat. No. 4,585,702 teaches a composition comprising magnetic particles and a lactone-acrylate adduct. The composition can include a photoinitiator such as 2,2-diethoxyacetophenone. The composition is coated onto a substrate and the solvent is allowed to evaporate with or without the use of thermal energy. The composition is then cured by exposure to ultraviolet or visible light. Also, see U.S. Pat. No. 4,555,449.
Solvent-based magnetic recording compositions are disadvantageous because after the composition is applied to a substrate, the solvent has to be allowed to evaporate. Also, the process is expensive because large volumes of solvent must be recovered. Ultraviolet curing of magnetic iron oxide recording compositions is also undesirable because the iron oxide absorbs ultraviolet radiation.